Include non-default ssh key location info

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/875

Provide help for people who aren't SSH-clued by indicating
how to point to key files that have been named something
other than the default. A lot of people seem to assume that
the filename they choose is irrelevant and then wonder why
their private key is not being found by simple 'ssh' commands.

doc/ssh/README.md

@@ -30,7 +30,7 @@ cat ~/.ssh/id_rsa.pub
 
 Copy-paste the key to the 'My SSH Keys' section under the 'SSH' tab in your
 user profile. Please copy the complete key starting with `ssh-` and ending
-with your username and host.  
+with your username and host.
 
 Use code below to copy your public key to the clipboard. Depending on your
 OS you'll need to use a different command:
@@ -77,3 +77,29 @@ information.
 ### Eclipse
 
 How to add your ssh key to Eclipse: http://wiki.eclipse.org/EGit/User_Guide#Eclipse_SSH_Configuration
+
+## Tip: Non-default OpenSSH key file names or locations
+
+If, for whatever reason, you decide to specify a non-default location and filename for your Gitlab SSH key pair, you must configure your SSH client to find your Gitlab SSH private key for connections to your Gitlab server (perhaps gitlab.com).
+For OpenSSH clients, this is handled in the `~/.ssh/config` file with a stanza similar to the following:
+
+```
+#
+# Main gitlab.com server
+#
+Host gitlab.com
+RSAAuthentication yes
+IdentityFile ~/my-ssh-key-directory/my-gitlab-private-key-filename
+```
+
+Another example
+```
+#
+# Our company's internal Gitlab server
+#
+Host my-gitlab.company.com
+RSAAuthentication yes
+IdentityFile ~/my-ssh-key-directory/company-com-private-key-filename
+```
+
+Due to the wide variety of SSH clients and their very large number of configuration options, further explanation of this topic is beyond the scope of this document.